Smaller electrolytic capacitors for implantable defibrillators

ABSTRACT

Implantable defibrillators are implanted into the chests of patients prone to suffering ventricular fibrillation, a potentially fatal heart condition. A critical component in these devices is an aluminum electrolytic capacitors, which stores and delivers one or more life-saving bursts of electric charge to a fibrillating heart. These capacitors make up about one third the total size of the defibrillators. Unfortunately, conventional manufacturers of these capacitors have paid little or no attention to reducing the size of these capacitors through improved capacitor packaging. Accordingly, the inventors contravened several conventional manufacturing principles and practices to devise unique space-saving packaging that allows dramatic size reduction. One embodiment of the invention uses thinner and narrower separators and top and bottom insulative inserts to achieve a 330-volt operating, 390-volt surge, 190-microfarad, 30-Joule aluminum electrolytic capacitor which is 33 percent smaller than conventional capacitors having similar electrical traits.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.09/843,053, filed on Apr. 26, 2001, now U.S. Pat. No. 6,535,374, whichis a division of U.S. patent application Ser. No. 09/165,848, filed onOct. 2, 1998, now issued as U.S. Pat. No. 6,275,729, the specificationsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention concerns electrolytic capacitors, particularlythose for use in medical devices, such as implantable defibrillators.

Every year more than half a million people in the United States sufferfrom heart attacks, more precisely cardiac arrests. Many of thesecardiac arrests stem from the heart chaotically twitching, orfibrillating, and thus failing to rhythmically expand and contract asnecessary to pump blood. Fibrillation can cause complete loss of cardiacfunction and death within minutes. To restore normal heart contractionand expansion, paramedics and other medical workers use a device, calleda defibrillator, to electrically shock a fibrillating heart.

Since the early 1980s, thousands of patients prone to fibrillationepisodes have had miniature defibrillators implanted in their bodies,typically in the left breast region above the heart. These implantabledefibrillators detect onset of fibrillation and automatically shock theheart, restoring normal heart function without human intervention. Atypical implantable defibrillator includes a set of electrical leads,which extend from a sealed housing into the heart of a patient afterimplantation. Within the housing are a battery for supplying power,heart-monitoring circuitry for detecting fibrillation, and a capacitorfor storing and delivering a burst of electric charge through the leadsto the heart.

The capacitor is typically an aluminum electrolytic capacitor, whichincludes two long strips of aluminum foil with two long strips of paper,known as separators, in between them. One of the aluminum foils servesas a cathode (negative) foil, and the other serves as an anode(positive) foil. Each foil has an aluminum tab, extending from its topedge, to facilitate electrical connection to other parts of thecapacitor.

The foil-and-paper assembly, known as the active element, is rolledaround a removable spindle or mandrel to form a cylinder and placed in around tubular case, with the two tabs extending toward the top of thecase. The paper is soaked, or impregnated, with a liquid electrolyte—avery electrically conductive solution containing positive or negativeions. And, the tubular case is sealed shut with a lid called a header.Extending from the header are two terminals connected respectively tothe anode foil and cathode foil via the aluminum tabs.

In recent years, manufacturers of aluminum electrolytic capacitors havefocused almost single-mindedly on improving the active element bydeveloping aluminum foils, electrolytes, and multiple-anode arrangementsthat improve capacitor performance, specifically energy density—theamount of energy or charge a capacitor stores per unit volume. Forexample, because energy density is directly proportional to the surfacearea of the aluminum foil making up the capacitive element,manufacturers have focused on methods of etching microscopic hills andvalleys into foils to increase their effective surface area.

In comparison, capacitor manufacturers have made little, if any, effortto improve packaging of the active element. For example, three leadingmanufactures of electrolytic capacitors—Rubycon, United Chemicon, andRoederstein—presently provide 330-360 volt, dual-anode aluminumelectrolytic capacitors which have total volumes greater than about 6.5cubic-centimeters (which is roughly the same size as a AA battery.) Yet,when the present inventors studied how this space was used, theydetermined that the ratio of the volume of the active element to theoverall volume of these capacitors was only about 40 percent. Thus, theinventors concluded that about 60 percent of the total capacitor volumewas wasted in the sense of failing to directly contribute to theperformance of these electrolytic capacitors.

Accordingly, the inventors identified an unmet need to reduce the sizeof electrolytic capacitors, especially those intended for implantabledefibrillators, through better packaging.

SUMMARY OF THE INVENTION

To address this and other needs, the inventors devised severalimprovements intended to reduce the overall size of electrolyticcapacitors, particularly those intended for implantable defibrillators.With these improvements, the inventors built an exemplary 360-voltoperating, 390-volt surge, 190-microfarad, 15.9-Joule aluminumelectrolytic capacitor about 33 percent smaller than conventionalcapacitors with comparable electrical traits.

One improvement contributing to this size reduction is the use of one ormore separators having a thickness less than the standard one-thousandthof an inch used in conventional electrolytic capacitors. The exemplaryembodiment uses combinations of paper separators with thicknesses of0.000787, 0.0005, and 0.00025 inches. For conventional cylindricallywound active elements, reducing separator thickness reduces the spacenecessary to contain the separators. In turn, this allows one to reducethe diameter and volume of the active element and thus the total volumeof the capacitor, or alternatively to increase the size of othercomponents of the active element to increase energy density for a giventotal volume.

In devising this improvement, the inventors recognized that theconventional practice of using thick paper separators stems from atleast three design objectives that are of lesser relevance toimplantable defibrillators. The first is that thicker paper reduceselectrolyte depletion, or evaporation, and thus generally increasescapacitor life. However, the inventors determined that electrolytedepletion has much less effect on capacitor life in medical deviceapplications than it does in the typical applications that govern howconventional electrolytic capacitors are built. In particular, implanteddefibrillators are generally not subject to the same long-termtemperature variations and extremes that conventional capacitors aredesigned to withstand.

Secondly, conventional manufacturers used the standard thick paperbecause it is less likely to tear or break during fabrication,particularly during the conventional high-speed process of winding thefoil-and-paper assembly around a spindle. Thus, using the thick paperallows conventional manufacturers to make capacitors faster. However,manufacturing speed is not very important to defibrillator makers whoneed to make many fewer capacitors than conventional manufacturers andthus can generally afford more time making them.

Thirdly, conventional manufacturers use the thick papers to reduce thechance of anode and cathode foils contacting each other and thereforecausing capacitor failure during functional testing. Since failedcapacitors are generally discarded or recycled, using thick papersultimately reduces manufacturing waste. However, waste is of lessconcern when making a small number of capacitors for implantabledefibrillators than it is when making millions of capacitors as do mostconventional manufacturers.

Another improvement contributing to the 33-percent size reduction is theuse of separators with end margins less than two millimeters. The endmargins are the portions of the separators which extend beyond the widthof the cathode and anode foils. Conventional paper separators are aboutfour-to-six millimeters wider than the aluminum foils of the activeelement, with the excess width typically divided to form equal top andbottom margins of two-to-three millimeters. Thus, when wound into a rolland stood up on one end, the top and bottom margins increase the overallheight of the active element and the overall height of the case neededto contain the active element.

Conventional manufacturers use the large end margins for at least tworeasons: to protect the foils from damage during high-speedmanufacturing processes, and to insulate the foils of the active elementfrom an aluminum case after insertion into the case. In particular,during high-speed winding, the foil and paper can easily becomemisaligned or skewed so that the edges of the foil extend beyond theedges of the papers, making them prone to bending, creasing, or tearing.The large, conventional end margins allow room for misalignment whilealso protecting the foil edges during high-speed winding. Afterinsertion into a tubular case, the end margins separate the edges of therolled foil from the top and bottom of the case, preventing theelectrically conductive case from shorting the anode and cathode foils.

In devising this improvement, the inventors determined that the endmargins could be greatly reduced, even eliminated completely in someembodiments, by more carefully winding the foils and separators duringmanufacture. Additionally, the inventors devised other ways ofinsulating foils from cases, while reducing capacitor size.

Specifically, the exemplary embodiment of the invention, which haslittle or no end margins, includes insulative inserts, for example, flatpaper disks, between the bottom of the active element and the bottom ofthe case and between the top of the active element and the underside ofa lid on the case. Other embodiments enclose substantially all of theactive element within an insulative bag.

Other improvements include reducing the thickness of the capacitor lid,or header, by about 50 percent, reducing the space between the undersideof the lid and the top of the active element, reducing the diameter ofthe normally empty mandrel region of the active element, and reducingthickness of the aluminum tube. Like the use of thinner separators,smaller end margins, and insulative inserts, these ultimately allowreductions in the size of electrolytic capacitors and implantabledefibrillators which incorporate them.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary aluminum electrolyticcapacitor 10 incorporating various space-saving features to achieve a33-percent size reduction over conventional electrolytic capacitors;

FIG. 2 is a cross-sectional view of electrolytic capacitor 10 takenalong line 2—2 of FIG. 1;

FIG. 3 is a cross-sectional view of a layered capacitive assembly 21used to form active element 20 of FIG. 2;

FIG. 4 is a perspective view of a unique foil structure 33 includedwithin some alternative embodiments of capacitive assembly 21;

FIG. 5 is a partial cross-sectional view of an insulative bag 40enclosing active element 20 in an alternative embodiment of capacitor10; and

FIG. 6 is a block diagram of generic implantable defibrillator 50including a capacitor that has one or more of the novel features ofcapacitor 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description, which references and incorporatesFIGS. 1-6, describes and illustrates one or more specific embodiments ofthe invention. These embodiments, offered not to limit but only toexemplify and teach, are shown and described in sufficient detail toenable those skilled in the art to implement or practice the invention.Thus, where appropriate to avoid obscuring the invention, thedescription may omit certain information known to those of skill in theart.

FIG. 1 shows a perspective view of an exemplary 360-volt operating,390-volt surge, 190-microfarad, 15.9-Joule (stored) electrolyticcapacitor 10 which incorporates various space-saving features of thepresent invention. Capacitor 10 has a diameter 10 d of about 14.5millimeters and a total height 10 h of about 30 millimeters, and a totalvolume of about five cubic-centimeters. Thus, capacitor 10 has an energydensity of about 3.2 Joules per cubic-centimeter.

In contrast, conventional electrolytic capacitors with comparableelectrical characteristics and of about the same diameter have heightsgreater than or equal to about 40 millimeters and total volumes greaterthan or equal to about 6.6 cubic-centimeters, with energy densitiesaround 2.4 Joules per cubic-centimeter. Thus, the exemplary capacitor isabout 33 percent smaller than conventional capacitors with similarelectrical traits.

More specifically, capacitor 10 includes a cylindrical aluminum case 12,a header (or lid) 14, and two aluminum terminals 16 and 18. Two rivets15 and 17 fasten terminals 16 and 18 to header 14. Aluminum case 12,which houses an active element 20 (not visible in this view), includes acircumferential seating groove 12 a and a rolled lip 12 b, both of whichsecure header 14 to case 12.

FIG. 2, a cross-section taken along line 2—2 in FIG. 1, shows that case12 has a thickness 12 t and that groove 12 a is spaced a distance 12 dfrom lip 12 b. In the exemplary embodiment, thickness 12 t is about0.010 inches, and distance 12 d is about 0.145 inches. Additionally,groove 12 a has a radius of about 0.035 inches, and lip 12 b, which isformed by rolling over the top edge of case 12, has a radius of about0.015 inches. Groove 12 a and lip 12 b each have a smaller radius thanthe corresponding features of conventional capacitors. In anotherembodiment, case 12 is vertically compressed to completely flatten orreduce the height of groove 12 a and thus to further reduce the heightand volume of capacitor 10.

FIG. 2 also shows that header 14 comprises two bonded layers 14 a and 14b and has a total thickness 14 t. Layer 14 a consists of rubber, andlayer 14 b consists of a phenolic resin. Although thickness 14 t isabout two millimeter in the exemplary embodiment, it ranges inclusivelybetween 0.5 to 2 millimeters in other embodiments. In contrast,conventional aluminum electrolytic capacitors use headers that are aboutthree to four millimeters thick.

FIG. 2 also shows that capacitor 10 includes an active element 20comprising about 19 turns of a layered capacitive assembly 21 aroundmandrel region 28 and two pairs of insulative inserts 30 a-30 b and 32a-32 b separating the top and bottom of active element 20 from interiorsurfaces of case 12. For clarity, FIG. 2 omits a plastic insulativesheath that surrounds the vertical surfaces of active element 20. In theexemplary embodiment, this sheath is a piece of transparent tape havinga width of 1.125 inches (or 28.6 millimeters).

FIG. 3, a cross sectional view of layered capacitive assembly 21, showsthat it includes a cathode 22, a three-foil anode 24, and fourelectrolyte-impregnated separators 26 a, 26 b, 26 c, and 26 d. Cathode22 and anode 24 each have a width (or height) 22 w, which partlydetermines a minimum height of case 12. Though not shown in FIG. 3 forclarity, cathode 22 and anode 24 also include insulative or dielectriccoatings, for example aluminum or tantalum oxide, on at least theirfacing surfaces. In this exemplary embodiment, cathode 22 and threeconstituent foils 24 a, 24 b, and 24 c of anode 24 are about 24millimeters wide and 100 micrometers thick. Cathode 22 is about 422millimeters long and anode 24 is about 410 millimeters long.

Although not shown in FIG. 3, anode foils 24 a, 24 b, and 24 c areconnected to a single aluminum anode tab 25 (which is shown in FIG. 2).Alternatively, individual anode tabs can be connected to each anodemembers, and to each other to form a joint or composite anode tab. Formore details on these or other types of tabs incorporated in otherembodiments of the invention, see U.S. Pat. Nos. 6,249,423 and6,110,233, which are respectively entitled Electrolytic Capacitor andMulti-Anodic Attachment and Wound Multi-Anode Electrolytic Capacitorwith Offset Anodes and which are incorporated herein by reference.

Anode tab 25, shown in FIG. 2, is ultrasonically welded to rivet 15 andthus electrically connected to terminal 16. In this embodiment, anodetab 25 is folded over itself; however, other embodiments omit this foldto reduce the space between header 14 and the top of active element 20.Though not visible in FIG. 2 or FIG. 3, cathode 22 includes a cathodetab which is similarly connected via rivet 17 to terminal 18.

Cathode 22 and anode foils 24 a, 24 b, and 24 c are made of anelectrically conductive material, such as aluminum or tantalum foil,with the anode etched to enhance its effective surface area. Examples ofsuitable etched foil structures include conventional core-etched andtunnel-etched foils, and a novel perforated-core-etched foil as well asvarious combinations of these foils. For instance, one embodiment formsanode 24 by stacking a core-etched or tunnel-etched foil with twoperforated-core-etched foils. FIG. 4 shows an example of aperforated-core-etched foil 33.

Foil 33 includes two opposing surfaces 33 a and 33 b that define anaverage foil thickness 33 t and a number of perforations, or holes, 33 pthat extend all the way through the foil. Surfaces 33 a and 33 b includerespective sets of surface cavities 34 a and 34 b, which have respectiveaverage maximum depths Da and Db and respective average cross-sectionalareas Sa and Sb (measured in a plane generally parallel to the foil). Inthe exemplary embodiment, the perforations, which are formed usinglaser, etch, or mechanical means, have an average cross-sectional areathat is 2-100 times larger than the average cross-sectional areas of thecavities. Depths Da and depths Db are approximately equal to one thirdor one quarter of thickness 33 t, and cross-sectional areas Sa and Sbare equal and range inclusively between about 0.16 and 0.36square-microns. The layout or arrangement of perforations can take anynumber of forms, including, for example, a random distribution or aspecific pattern with each perforation having a predetermined positionrelative to other perforations. Perforations 33 p, which can be anyshape, for example, circular, have a cross-sectional area rangingbetween approximately 500 square-microns and 32 square-millimeters inthe exemplary embodiment. Additionally, the exemplary embodiment limitsthe total surface area of perforations 10 p to about 20 percent of thetotal area of foil 33.

The perforated-coil-etched foil can be made either by perforating aconventional core-etched foil or core-etching a perforated foil. Furtherdetails of the perforated core-etched foil are disclosed in co-pendingU.S. patent application Ser. No. 09/165,779, filed on Oct. 2, 1998,entitled High-Energy Density Capacitors for Implantable Defibrillators.This application was filed on the same day as the present applicationand is incorporated herein by reference.

In addition to cathode 22 and three-part anode 24, FIG. 3 shows thatcapacitive assembly 21 includes thin electrolyte-impregnated separators26, specifically 26 a, 26 b, 26 c, and 26 d. Separators 26 a, 26 b, 26c, and 26 d, each of which consists of kraft paper impregnated with anelectrolyte, such as an ethylene-glycol base combined withpolyphosphates or ammonium pentaborate, distinguish in at least two waysfrom separators used in conventional electrolytic capacitors.

First, in contrast to conventional separators which are one-thousandthof an inch or more in thickness to improve fabrication yield and reduceelectrolyte depletion, separators 26 a-26 d are each less thanone-thousandth of an inch in thickness. In the exemplary embodiment,each of the separators has one of the following thicknesses: 0.000787,0.0005 inches, and 0.00025 inches, with thicker papers preferably placednearer the center of the active element to withstand the greater tensilestress that interior separators experience during winding.

However, various other embodiments of the invention use combinations ofthese thicknesses, combinations of these thickness with otherthicknesses, and combinations of other thicknesses. Additionally, otherembodiments of invention combine one or more thin separators with one ormore conventional separators. Ultimately, the use of one or more thinnerseparators reduces the diameter of the active element for a given lengthof separator (assuming all other factors are equal).

Second, in contrast to conventional separators which are about four tosix millimeters wider than the anode and cathode foils to provide largetwo to three millimeter end margins, separators 26 have a width 26 wwhich is less than four millimeters wider than cathode 22 and anode 24to provide smaller end margins 27 a and 27 b. For example, in theexemplary embodiment, width 26 w is about 27 millimeters, or threemillimeters wider than cathode 22 and anode 24, to provide end margins27 a and 27 b of about 1.5 millimeters. Other embodiments of theinvention provide at least one end margins of about 1.75, 1.25, 1, 0.75,0.5, 0.25, and even 0.0 millimeters.

The large end margins of conventional separators are necessary toprevent damage to foil areas during high-speed fabrication and toinsulate the cathode and anode foils from case 12. However, theinventors recognized that they are not necessary in all applications,particularly defibrillator applications, where high-speed fabrication isof little concern or where the inventors have devised other ways ofinsulating the foils from the top and bottom of aluminum case 12.

In particular, FIG. 2 shows that the exemplary embodiment provides twopairs of insulative inserts 30 a-30 b and 32 a-32 b, which prevent otherconductive portions of capacitor 10, specifically anode tab 25 andrivets 15 and 17 and the interior surface of case 12, from shortingcathode 22 and anode 24. In the exemplary embodiment, these inserts aretwo pairs of paper disks, with each disk having a thickness of oneone-thousandth of an inch and a diameter of about 14 millimeters.However, other embodiments of the invention use not only thinner orthicker inserts, but also different insert materials and numbers ofinserts. For example, in one alternative embodiment, one or both pairsof inserts 30 a-30 b and 32 a-32 b consist of a polymeric insulator, andin another embodiment, inserts 30 a and 30 b consist of differentmaterial combinations, such as paper and a polymeric insulator.

As an alternative to insulative inserts, other embodiments enclosesubstantially all of active element 20 within an insulative bag. FIG. 5shows an exemplary embodiment of an insulative bag 40 enclosingsubstantially all of active element 20, with the exception of the anodeand cathode tabs. In this embodiment, bag 40 comprise materials similarto the insulative inserts.

FIG. 2 also shows that capacitive assembly 21 of active element 20 iswound around a mandrel (not shown), which has been removed after windingto leave an empty mandrel region or cavity 28. In this exemplaryembodiment, mandrel region 28 has a width or diameter of about 2.5millimeters, or more generally less than about 3.5 millimeters. Incontrast to conventional electrolytic capacitors which have mandrels ormandrel regions with 3.5-millimeter diameters, the smaller mandrels ofthe present invention allow use of about 2-5 percent more aluminum foilwithout increasing the total volume of the capacitor. Another embodimentof the invention uses about the same amount of foil as conventionalcapacitors with the smaller mandrel region, thereby reducing thediameter of the active element without reducing energy density.

Mandrels with diameters less than 3.5 millimeters are not used inmanufacturing conventional electrolytic capacitors primarily becausethey increase the difficulty in rolling the cathodes, anodes, andseparators around them. Indeed, a smaller-diameter mandrel increases thetensile stress on the cathode, anode, and separators, leading them tobreak or tear during high-speed winding and thus to increasemanufacturing waste. In addition, the smaller diameter mandrels tend tobreak and require replacement more often than larger mandrels. Thus,conventional capacitor manufactures avoid smaller mandrels to increasemanufacturing yield and to accelerate manufacturing. However, theseconventional objectives are of lesser importance when making smallnumbers of capacitors for implantable medical devices, specificallydefibrillators.

Exemplary Embodiment of Implantable Defibrillator

FIG. 6 shows one of the many applications for space-saving electrolyticcapacitor 10: a generic implantable defibrillator 50. More specifically,defibrillator 50 includes a lead system 52, which after implantationelectrically contacts strategic portions of a patient's heart, amonitoring circuit 54 for monitoring heart activity through one or moreof the leads of lead system 52, and a therapy circuit 56 which deliverselectrical energy through lead system 52 to the patient's heart. Therapycircuit 56 includes an energy storage component 56 a which incorporatesat least one capacitor having one or more of the novel features ofcapacitor 10. Defibrillator 50 operates according to well known andunderstood principles.

In addition to implantable defibrillators, the innovations of capacitor10 can be incorporated into other cardiac rhythm management systems,such as heart pacers, combination pacer-defibrillators, anddrug-delivery devices for diagnosing or treating cardiac arrhythmias.They can be incorporated also into non-medical applications, forexample, photographic flash equipment. Indeed, the innovations ofcapacitor 10 are pertinent to any application where small, high energy,low equivalent-series-resistance (ERS) capacitors are desirable.

Conclusion

In furtherance of the art, the inventors have devised uniquespace-efficient packaging for aluminum electrolytic capacitors whichallows either reduction of the actual size (total volume) of capacitorswith specific electrical traits or improvement in the electrical traitsof capacitors of a specific total volume. For example, in theirexemplary embodiment, the inventors use thinner and narrower separatorsand top and bottom insulative inserts to achieve a capacitor which isabout 33 percent smaller than conventional capacitors having similarelectrical traits.

The embodiments described above are intended only to illustrate andteach one or more ways of practicing or implementing the presentinvention, not to restrict its breadth or scope. The actual scope of theinvention, which embraces all ways of practicing or implementing theconcepts and principles of the invention, is defined only by thefollowing claims and their equivalents.

1. An electrolytic capacitor comprising: an active element having ananode and a cathode, with one or more separators separating the anodefrom the cathode; a conductive case enclosing the active element; and aninsulative bag substantially enclosing and separating the active elementfrom the conductive case.
 2. The electrolytic capacitor of claim 1wherein one or more of the separators has a nominal thickness of0.000787, 0.0005, or 0.00025 inches and comprises paper.
 3. Theelectrolytic capacitor of claim 1 wherein one or more of the separatorshave a width and wherein the capacitor further includes one or more foilmembers having a width that is at most 3.5 millimeters less than thewidth of one or more of the separators.
 4. The electrolytic capacitor ofclaim 1 wherein the active element has top and bottom portions and thecase has a bottom interior surface adjacent the bottom portion of theactive element and an opening adjacent the top portion of the activeelement and wherein the capacitor further comprises a header positionedat least partly within the opening of the case.
 5. The electrolyticcapacitor of claim 4 wherein the case is cylindrical.
 6. Theelectrolytic capacitor of claim 4 wherein the header has a thicknessless than about 2.5 millimeters.
 7. The electrolytic capacitor of claim4 wherein the case includes a circumferential seating groove which hasbeen partially or completely flattened to further reduce case height. 8.The electrolytic capacitor of claim 1 wherein the separators are part ofa cylindrical active element having a mandrel or mandrel region whichhas a width or diameter less than about 2.5 millimeters.
 9. Theelectrolytic capacitor of claim 1 wherein the electrolytic capacitor isan aluminum electrolytic capacitor.
 10. The electrolytic capacitor ofclaim 1 wherein the capacitor has a nominal capacitance of at least 190micro-farads, a voltage rating of at least 300 volts, and a total volumeless than about 6 cubic-centimeters.
 11. The electrolytic capacitor ofclaim 10 wherein the total volume is approximately 5 cubic-centimeters.12. The electrolytic capacitor of claim 1, wherein the insulative bagcomprises a polymeric material.
 13. An electrolytic capacitorcomprising: a cylindrical active element that includes a capacitiveassembly having one or more separators and one or more foil members,with one or more of the separators having a width and one or more of thefoil members having a width that is at most 3.5 millimeters less thanthe width of one or more of the separators; a conductive case enclosingthe active element; and an insulative bag substantially enclosing andseparating the active element from an interior surface of the conductivecase.
 14. The electrolytic capacitor of claim 13 wherein the width ofthe one or more of the foil members is about 2.5 millimeters less thanthe width of the one or more of the separators.
 15. The electrolyticcapacitor of claim 13, wherein the insulative bag comprises means forenclosing and separating the active element from the interior surface ofthe conductive case.
 16. An electrolytic capacitor comprising: acylindrical active element having a top and a bottom portion; acylindrical case at least partly encasing the active element and havingan opening adjacent the top portion of the active element; a headerpositioned at least partly within the opening of the case; and means forcontaining and separating the active element from the cylindrical case.17. The electrolytic capacitor of claim 16 wherein the header has athickness less than about 2.5 millimeters.
 18. An aluminum electrolyticcapacitor having a nominal capacitance of at least 190 micro-farads, avoltage rating of at least 300 volts, a total volume less than about 6cubic-centimeters, wherein the capacitor comprises: a cylindrical activeelement having a top and a bottom portion; a cylindrical case at leastpartly encasing the active element and having a bottom interior surfaceadjacent the bottom portion of the active element and an openingadjacent the top portion of the active element; a header positioned atleast partly within the opening of the case; and means for containingand separating the active element from the cylindrical case.
 19. Thealuminum electrolytic capacitor of claim 18 wherein the total volume isapproximately 5 cubic-centimeters.